Expandable shelter hvac systems

ABSTRACT

Expandable shelters having a heating, ventilation, and air conditioning (HVAC) system arranged to receive outside air away from a mechanical compartment are disclosed. The expandable shelters may comprise an air inlet vent disposed in a front of the expandable shelter interconnected to an in-floor air duct arranged to draw outside air below an interior floor and exchange heat with the coolest area of the expandable shelter. By virtue of having an air inlet vent receive outside air from a location substantially away from the mechanical compartment and exchange heat with the coolest area of the expandable shelter, an environmental control unit (ECU), housed in the mechanical compartment, receives relatively cool outside air, keeping air temperatures inside the mechanical compartment below the upper operating limit of the ECU.

BACKGROUND

Expandable shelters exist that have internal environmental control units(ECUs). For example, expandable shelters exist that have a mechanicalroom that houses an ECU for heating and/or cooling an interior of theexpandable shelter. If airflow to the mechanical room is inadequate whenequipment (i.e., ECUs, engines, and/or generators, etc.) housed in themechanical room is in use, temperatures inside the mechanical room canexceed an upper operating limit of the ECU. Inadequate airflow to theECU can cause the ECU to operate inefficiently and/or stop producingcool air altogether.

Accordingly, there remains a need in the art for improved airflow to anECU housed in a mechanical room of an expandable shelter.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is set forth with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different figures indicates similaror identical items.

FIG. 1 depicts a top view of an illustrative expandable shelter havingan environmental control unit (ECU) housed in a mechanical compartmentat a back end of the expandable shelter and an air inlet vent disposedat an exterior of a front end of the expandable shelter.

FIG. 2 depicts an illustrative view of the mechanical compartment at theback end of the expandable shelter illustrated in FIG. 1.

FIG. 3 depicts an illustrative view of the air inlet vent at the frontend of the expandable shelter illustrated in FIG. 1.

FIG. 4A is a line chart illustrating test results showing an ECUperformance prior to implementing a heating ventilation air conditioning(HVAC) system of the expandable shelter illustrated in FIGS. 1-3.

FIG. 4B is a line chart illustrating test results showing an increase inthe ECU performance as a result of implementing the heating ventilationair conditioning (HVAC) system of the expandable shelter illustrated inFIGS. 1-3.

DETAILED DESCRIPTION Overview

This application describes expandable shelters having a heating,ventilation, and air conditioning (HVAC) system arranged to receiveoutside air from a location distant from a mechanical compartment of theexpandable shelters. By virtue of having an HVAC system arranged toreceive outside air from a location distant from a mechanicalcompartment, an environmental control unit (ECU), housed in themechanical compartment, receives pure outside air and keeps airtemperatures below the upper operating limit of the ECU.

In one example, the expandable shelters may comprise an air inlet ventdisposed in an exterior of a front of the expandable sheltersubstantially away from the mechanical compartment arranged in a back ofthe expandable shelter.

In some examples, the inlet vent may be interconnected to an in-floorair duct arranged to draw the outside air below an interior floor of theexpandable shelter to exchange heat with the interior floor and coolerair located below the expandable shelter.

In some examples, the expandable shelter may comprise an insulated airduct arranged in the mechanical compartment. The insulated air duct maybe interconnected to the in-floor air duct and arranged to insulate theoutside air from heat contained in the mechanical compartment whileproviding the cooler outside air to the ECU.

In some examples, the HVAC system described herein may include a boosterfan to increase airflow to or through the ECU. For example, a boosterfan may be fixed to the ECU arranged in the mechanical compartment.

While the air inlet vents are described in various embodiments herein asbeing located proximate to a bottom and a center of the front exteriorof the expandable shelter, the air inlet vents may be located at otherlocations on the front exterior of the expandable shelter. For example,the air inlet vents may be located proximate to a bottom left sideand/or a bottom right side of the front exterior of the expandableshelter. Alternatively, the air inlet vents may be located along all orsubstantially all of the bottom front exterior of the expandableshelter.

While the expandable shelters are described in various embodimentsherein as having expandable sides between the front and back ends, theexpandable shelters may have other expandable portions. For example, theexpandable shelters may additionally or alternatively comprise anexpandable top, front, and/or back, or any combination thereof.

Illustrative Expandable Shelter HVAC Systems

FIG. 1 depicts a schematic top view of an illustrative expandableshelter 102 having an environmental control unit (ECU) 104, with a topof the shelter 102 removed to show internal components of the shelter.The ECU 104 may be housed in a mechanical compartment 106 at a back end108, opposite a front end 110, of the expandable shelter 102. Themechanical compartment 106 may be accessed via two louvered doors 112(A)and 112(B). The louvered doors 112(A) and 112(B) may provide forventilating the mechanical compartment 106. For example, the ECU 104 mayexhaust hot air out at least one of the louvered doors 112(A) and112(B).

The expandable shelter 102 may include an air inlet vent 114 disposed atan exterior of the front end 110 opposite to the mechanical compartment106. The air inlet vent 114 may take in or receive ambient outside airat the front end 110 of the expandable shelter 102. Because the airinlet vent 114 is disposed on the front end 110, opposite to the backend 108 of the expandable shelter 102, this eliminates any chance oftaking in hot air exhausted from the mechanical compartment 106. Forexample, because the air inlet vent 114 is disposed on the front end110, the air inlet vent 114 does not take in hot exhaust from anengine/generator, an ECU (e.g., ECU 104), or any other heat generatingequipment housed by the mechanical compartment 106 at the back end 108of the expandable shelter 102.

The expandable shelter 102 may include an enclosure 116 defining aninterior 118. The enclosure 116 may include sides 120(A) and 120(B),which may be displaceable in order to expand the shelter from astorage/shipping condition to a deployed/use position. For example, thesides 120(A) and 120(B) may be displaceable out and away from theenclosure 116, as indicated by direction arrows 122(A) and 122(B), toprovide additional interior space 124(A) and 124(B) during use.

The expandable shelter 102 may be equipped to be used in variousenvironments. For example, the expandable shelter 102 may be equippedfor use in a commercial environment, industrial environment, militaryenvironment, or other environments. By way of example and notlimitation, the expandable shelter 102 may be equipped to be used as afield office, field hospital, decontamination station, jail/brig,holding cell, isolation ward, command post, field morgue, communicationcenter, camp, laboratory, and/or school. Further, the expandable shelter102 may be equipped for use in most conditions. For example, theexpandable shelter 102 may be equipped for use in desert conditions,arctic conditions, and/or marine conditions.

The expandable shelter 102 may be at least partially constructed from astandard shipping container (e.g., intermodal freight container) formedof metal (e.g., steel). For example, the enclosure 116 may be a standardshipping container modified to include the expandable sides 120(A) and120(B), the mechanical compartment 106, electrical components, plumbing,insulation, etc. Because the expandable shelters 102 may be constructedfrom a standard shipping container, the expandable shelter 102 may havedimensions similar to that of standard shipping containers. For example,the expandable shelter 102 may have a length of at least about 20 feet(6 meters) and at most about 40 feet (12 meters), a width of at leastabout 8 feet (2 meters) and at most about 10 feet (3 meters), and aheight of at least about 8 feet (2 meters) and at most about 10 feet (3meters). However, in other examples, expandable shelters according tothis disclosure may have other larger or smaller dimensions.

The expandable shelter 102 may include in-floor air ducts 126(A) and126(B) interconnected to the air inlet vent 114. The in-floor air ducts126(A) and 126(B) may be arranged to draw outside air from the front end110 to the back end 108 along a bottom center (line A-A′) of theenclosure 116. The in-floor air ducts 126(A) and 126(B) may be at leastpartially formed of an interior floor 128 of the expandable shelter 102fixed to structural members 130(1) 130(2), 130(3), 130(4), and 130(N).For example, the in-floor air ducts 126(A) and 126(B) may be arrangedbelow the floor 128 and between any of the structural members130(1)-130(N). For example, the in-floor air ducts 126(A) and 126(B) maybe arranged below the floor 128 and between the structural members whichare located substantially proximate to the bottom center (line A-A′) ofthe expandable shelter 102. While the in-floor air ducts 126(A) and126(B) are illustrated as being arranged between the structural members130(2), 130(3), and 130(4), in other embodiments the in-floor air duct126(A) and 126(B) may additionally or alternatively be arranged betweenstructural members 130(1) and 130(2), and/or 130(4) and 130(N),respectively, or any other combination of structural members130(1)-130(N).

The floor 128 may comprise strips (e.g., tongue and groove planks) ofmaterial, a single sheet of material, or multiple sheets of materialfixed to the structural members 130(1)-130(N). For example, the floor128 may be formed of sheets of fiberglass, plastic, metal, wood, carbonfiber, or composites thereof (e.g., fiberglass reinforced plywood), andfixed to the structural members 130(1)-130(N). The floor 128 may befixed to the structural members 130(1)-130(N) via a mechanical fastener(e.g., screws and/or bolts), a weld, an adhesive, or the like. Thestructural members 130(1)-130(N) may comprise beams (I-beams,wide-flange beams, C-channel beams, etc.), rails, tubes, pipes, etc. Thestructural members 130(1)-130(N) may be formed of any material suitablefor carrying loads. For example, the structural members 130(1)-(N) maybe formed of metal (e.g., steel), wood, reinforced concrete, composite,plastic, carbon fiber, etc. The structural members 130(1)-(N) may befixed to the enclosure 116. For example, the structural members130(1)-(N) may be mechanically fastened, welded, adhered, or the like,to a portion of the enclosure 116.

Because the in-floor air ducts 126(A) and 126(B) may be arranged to drawthe outside air below the floor 128, the in-floor air ducts 126(A) and126(B) are arranged to exchange heat with the floor 128 of theexpandable shelter 102. Further, because the in-floor air ducts 126(A)and 126(B) may be arranged proximately along the bottom center (lineA-A′) of the expandable shelter 102, the in-floor air ducts 126(A) and126(B) may be arranged in the coolest area of the expandable shelter102. Thus, the in-floor air ducts 126(A) and 126(B) draw outside ambientair under the floor 128 through the coolest area of the expandableshelter 102, back to the mechanical compartment 106. As the in-floor airduct 126(A) and 126(B) draws outside ambient air under the floor 128through the coolest area of the expandable shelter 102, the in-floor airducts 126(A) and 126(B) may provide for exchanging heat with the floor128 and/or the structural members 130(1)-130(N). For example, becausethe interior floor 128 and/or the structural members 130(1)-130(N) maybe cooler than the outside ambient air, the outside ambient air mayexchange heat with the floor 128 and/or the structural members130(1)-130(N) as the in-floor air ducts 126(A) and 126(B) draw theoutside air below the floor 128, proximate to the bottom center (lineA-A′), back to the mechanical compartment 106. Further, the air underthe expandable shelter 102 and close to the ground may also be coolerand may therefore cool the incoming air. For example, because the airunder the expandable shelter 102 and close to the ground may be coolerthan the outside ambient air, the outside ambient air may exchange heatwith the structural members 130(1)-130(N) as the in-floor air ducts126(A) and 126(B) draw the outside air below the floor 128 back to themechanical compartment 106.

FIG. 2 is a perspective view of the mechanical compartment 106 at theback end 108 of the expandable shelter 102 illustrated in FIG. 1. Asdiscussed above with respect to FIG. 1, the in-floor air ducts 126(A)and 126(B) may be arranged along the bottom center (line A-A′) of theexpandable shelter 102, in the coolest area of the expandable shelter102. An insulated air duct 202 may be arranged vertically in themechanical compartment 106 and interconnected to the in-floor air ducts126(A) and 126(B). For example, the insulated air duct 202 may bearranged substantially perpendicular to the in-floor air ducts 126(A)and 126(B) and may receive outside air from the in-floor air ducts126(A) and 126(B). The insulated air duct 202 may be arranged toinsulate the outside air received from the in-floor air ducts 126(A) and126(B). For example, the insulated air duct 202 may include an outershell encasing an inner shell and an insulation material disposedbetween the outer and inner shells. The outer and inner shells may beformed of a metal (e.g., stainless steel), plastic, or composite.

The insulated air duct 202 may insulate the received outside air fromheat contained in the mechanical compartment 106. For example, theinsulated air duct 202 may insulate the received outside air from heatgenerated from an engine/generator, an ECU (e.g., ECU 104), or any otherheat generating equipment housed by the mechanical compartment 106.

FIG. 2 illustrates the mechanical compartment 106 as including a shelf204. The shelf 204 may partition the mechanical compartment 106 into twocompartments 206(A) and 206(B). The ECU 104 may rest on the shelf 204 inthe compartment 206(B) above the compartment 206(A). The compartment206(A) may house at least an engine/generator and/or other equipment.Further, when the louvered doors 112(A) and 112(B) are closed, the ECU104 is enclosed in the compartment 206(B) and the engine/generatorand/or other equipment is enclosed in the compartment 206(A).

The insulated air duct 202 may extend through the compartment 206(A) andinto the compartment 206(B). For example, the insulated air duct 202 mayextend through the compartment 206(A) and terminate at a vent 208 in theshelf 204. The insulated air duct 202 may deliver the cool outside airinto the compartment 206(B) to cool the ECU 104. For example, theinsulated air duct 202 may deliver the outside air into the compartment206(B) where a booster fans 210(A) and 210(B), fixed to the ECU 104,help the outside air across a condenser of the ECU 104. In addition toenhancing the airflow across the condenser of the ECU, the booster fans210(A) and 210(B) may counteract a head loss due to restriction of theoutside air flowing from the front end 110 of the expandable shelter 102to the back end 108 of the expandable shelter 102. For example, boosterfan 210(A) may be a large squirrel cage fan fixed to the ECU 104 thatpulls the air from the in-floor air ducts 126(A) and 126(B), and upthrough the insulated air duct 202 and injects the air toward thecondenser. The booster fan 210(B) may be an axial fan(s) fixed to theback of the condenser of the ECU 104 to counteract a restriction of airflow across the condenser. Generally, the booster fan 210(A) helps drawthe outside air from the air inlet vent 114, along the in-floor airducts 126(A) and 126(B), and up through the insulated air duct 202 tothe compartment 206(B) enclosing the ECU 104, while the booster fan(s)210(B) pull the air across the condenser and push the air out thelouvered door 112(B).

FIG. 3 depicts an illustrative view of the air inlet vent 114 at thefront end 110 of the expandable shelter 102 illustrated in FIG. 1. Asdiscussed above with respect to FIG. 1, the air inlet vent 114 may bedisposed at an exterior 302 of the front end 110 of the expandableshelter 102 to receive outside air substantially away from themechanical compartment 106.

While FIG. 3 illustrates the air inlet vent 114 as being four separateopenings disposed at the exterior 302, the air inlet vent 114 may be anynumber of openings disposed at the exterior 302. For example, the airinlet vent 114 may be one opening disposed at the exterior 302. The airinlet vent 114 may include an air filter to prevent debris fromcontaminating the heating, ventilation, air conditioning (HVAC) systemof the expandable shelter 102 (i.e., the air inlet vent 114, in-floorair ducts 126(A) and 126(B), insulated air duct 202, compartment 206(B),booster fans 210(A) and 210(B), and ECU 104). The air filter may be ahog hair filter, a paper filter, foam filter, a cotton filter, wire meshfilter, etc. The air inlet vent 114 may include a screen to preventanimals from entering the HVAC system. Further, the air inlet vent 114may include a snorkel. For example, the air inlet vent 114 may include asnorkel that removeably couples to the air inlet vent 114, raising theair inlet vent 114 up and away from the ground. For example, a snorkelmay be removeably coupled to the inlet vent 114 to ensure the air inletvent 114 remains open and free of any obstructions (e.g., dirt, mud,sand, foliage, water, or the like). The snorkel may be insulated andextend up against the exterior 302 of the front end 110 of theexpandable shelter 102. For example, a snorkel may extend a distance ofabout ⅛, ¼, ⅓, ½, etc., the height of the expandable shelter 102.

A passageway 304 may be disposed at the exterior 302 of the front end110 of the expandable shelter 102. The passageway 304 may provide accessto the interior 118 of the enclosure 116, and/or access to the interiors124(A) and 124(B) of the expandable sides 120(A) and 120(B). Thepassageway 304 may be arranged above the air inlet vent 114. Forexample, the passageway 304 may be arranged above the bottom center(line A-A′) of the expandable shelter 102.

Objective Evidence

FIG. 4A is a line chart 402 illustrating test results showing an ECUperformance prior to implementing a heating ventilation air conditioning(HVAC) system of the expandable shelter illustrated in FIGS. 1-3. Forexample, FIG. 4A illustrates test results with an engine/generator andan environmental control unit (ECU) (e.g., ECU 104) running behindclosed louvered doors (e.g., louvered doors 112(A) and 112(B)) in anexpandable shelter, in which an air inlet for the ECU is disposedproximate to, and on a same side of the expandable shelter as, theexhaust of the ECU. That is, the chart 402 of FIG. 4A corresponds to anexpandable shelter without an air inlet vent (e.g., air inlet vent 114)disposed at an exterior (e.g., exterior 302) of a front end (e.g., frontend 110) of the expandable shelter. Further, FIG. 4A illustrates testresults with an engine/generator and an ECU running behind closedlouvered doors in an expandable shelter without an in-floor air duct(e.g., in-floor air ducts 126(A) and 126(B)) interconnected to the airinlet vent arranged to draw outside air from the front end a back end(e.g., back end 108) along a bottom center (e.g., bottom center (lineA-A′)) of the expandable shelter.

The line chart 402 includes a vertical axis 404 representing a coolingair temperature, in five degree increments, on an evaporator/exhaustside of the ECU, and a horizontal axis 406 representing ambient airtemperature, in five degree increments, on the condenser/inlet side ofthe ECU.

The line chart 402 illustrates a trend line 408, which generally showsthe ECU providing cooling air until the ambient air temperature on thecondenser side is about 120 degrees. That is, the test data shows theECU, housed in a mechanical compartment with poor airflow through thelouvered doors. As a result, the ECU substantially stops cooling theinterior of the expandable shelter when outside ambient temperaturesreach or exceed 120 degrees Fahrenheit.

FIG. 4B is a line chart 410 illustrating test results showing anincrease in the ECU performance subsequent to implementing the heatingventilation air conditioning (HVAC) system of the expandable shelterillustrated in FIGS. 1-3. For example, FIG. 4B illustrates test resultswith an engine/generator and the ECU running in the expandable shelterincluding the air inlet vent and the in-floor air ducts interconnectedto the air inlet vent arranged to draw outside air from the front endthe back end along the bottom center of the expandable shelter.

The line chart 410 includes a vertical axis 412 again representing acooling air temperature, in five degree increments, on theevaporator/exhaust side of the ECU, and a horizontal axis 414representing ambient air temperature, in five degree increments, on thecondenser/inlet side of the ECU.

The line chart 410 illustrates a trend line 416, which generally showsthe ECU providing cooling air until the ambient air temperature on thecondenser side exceeds about 150 degrees. That is, the test data showsthe ECU, housed in a mechanical compartment with a substantiallyimproved airflow as compared to line chart 402. As a result, the ECUcontinues to cool the interior of the expandable shelter up to when theoutside ambient temperature is about 150 degrees Fahrenheit.

Thus, lab tests have demonstrated an ECU, installed in the expandableshelter HVAC system described above with respect to FIGS. 1-3,continuing to provide cool air in substantially hotter conditions thanwere possible by ECUs installed in conventional shelter systems.

CONCLUSION

Although embodiments have been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the disclosure is not necessarily limited to the specific featuresor acts described. Rather, the specific features and acts are disclosedas illustrative forms of implementing the embodiments. For example, invarious embodiments, any of the structural features and/ormethodological acts described herein may be rearranged, modified, oromitted entirely. For example, the shape, size, and configuration of theexpandable shelter may be varied.

What is claimed is:
 1. An expandable shelter comprising: a mechanicalcompartment arranged in an end of the expandable shelter housing atleast an environmental control unit (ECU) of a heating, ventilation, andair conditioning (HVAC) system; and an air inlet vent of the HVAC systemdisposed at an exterior of another end of the expandable shelteropposite to the end of the expandable shelter having the mechanicalcompartment, wherein the air inlet is to receive outside airsubstantially away from the mechanical compartment.
 2. The expandableshelter system of claim 1, further comprising: a floor arranged in aninterior of the shelter; and an air duct of the HVAC system arrangedbelow the floor from the end to the other end, wherein the air duct isinterconnected to the air inlet and arranged to draw outside air fromthe air inlet vent to the ECU through the air duct below the floor andto exchange heat with the interior of the shelter through the floor. 3.The expandable shelter system of claim 1, further comprising: aninsulated air duct of the HVAC system arranged in the mechanicalcompartment, wherein the insulated duct is interconnected to the airduct below the floor and arranged to insulate the received outside airfrom heat contained in the mechanical compartment and to provide thereceived outside air to the ECU.
 4. The expandable shelter system ofclaim 1, further comprising a booster fan to draw the received outsideair from the air inlet vent to the ECU and to push the received outsideair across a condenser of the ECU.
 5. An expandable shelter comprising:an enclosure defining an interior and including a top, bottom, front,back, and two sides, at least one of the sides being displaceable outand away from the enclosure; a mechanical compartment arranged in theback of the enclosure and housing an environmental control unit (ECU) ofa heating, ventilation, and air conditioning (HVAC) system; an air inletvent of the HVAC system disposed proximate to the bottom of theenclosure and in an exterior of the front to receive outside air; and anin-floor air duct of the HVAC system interconnected to the air inlet andarranged to draw the received outside air from the front to the back andalong the bottom of the enclosure, and to exchange heat with theinterior of the enclosure.
 6. The expandable shelter of claim 5, furthercomprising: a floor fixed to structural members arranged from the frontto the back and along the bottom of the enclosure, wherein the in-floorair duct is arranged below the floor and between the structural membersto exchange heat with the floor in the interior of the enclosure.
 7. Theexpandable shelter of claim 6, wherein at least one of the structuralmembers is formed of a metal beam and at least a portion of the floor isformed of a composite sheet.
 8. The expandable shelter of claim 5,further comprising an insulated air duct of the HVAC systeminterconnected to the in-floor air duct, the insulated air duct housedin the mechanical compartment and arranged to insulate the receivedoutside air from heat contained in the mechanical compartment and toprovide the received outside air to the ECU.
 9. The expandable shelterof claim 8, wherein the insulated air duct comprises an outer shellencasing an inner shell and an insulation material disposed between theouter and inner shells.
 10. The expandable shelter of claim 9, whereinthe outer and inner shells are formed of metal, plastic, or composite.11. The expandable shelter of claim 9, wherein the outer and innershells are formed of steel.
 12. The expandable shelter of claim 5,further comprising an air filter arranged in the air inlet vent toprevent debris from contaminating the HVAC system.
 13. The expandableshelter of claim 12, wherein the air filter arranged in the air inletcomprises a hog hair filter, a paper filter, foam filter, a wire meshfilter, or a cotton filter.
 14. The expandable shelter of claim 5,further comprising a screen arranged in the air inlet vent to preventanimals from entering the HVAC system.
 15. A heating, ventilation, andair conditioning (HVAC) system for use in an expandable shelter,comprising: an environmental control unit (ECU) housed in a mechanicalcompartment arranged in a back of the expandable shelter opposite to afront of the expandable shelter; and a duct system for supplying air tothe ECU, the duct system comprising: an air inlet vent disposed in anexterior of the front of the expandable shelter to receive outside airfrom a location substantially away from the mechanical compartment inthe back of the expandable shelter; an in-floor air duct arranged belowan interior floor of the expandable shelter, wherein the in-floor airduct is interconnected to the air inlet and arranged to draw thereceived outside air below the interior floor and to exchange heat withthe interior of the shelter through the floor; and an insulated air ductarranged in the mechanical compartment, wherein the insulated air ductis interconnected to the in-floor air duct and arranged to insulate thereceived outside air from heat contained in the mechanical compartmentwhile providing the received outside air to the ECU.
 16. The heating,ventilation, and air conditioning (HVAC) system for use in an expandableshelter of claim 15, further comprising a booster fan fixed to the ECUto help draw the received outside air from the air inlet vent throughthe in-floor air duct and the insulated air duct to the ECU and to pushthe received outside air across a condenser of the ECU.
 17. The heating,ventilation, and air conditioning (HVAC) system for use in an expandableshelter of claim 15, wherein the insulated air duct comprises an outershell encasing an inner shell and an insulation material disposedbetween the outer and inner shells.
 18. The heating, ventilation, andair conditioning (HVAC) system for use in an expandable shelter of claim15, wherein the outer and inner shells are formed of steel.
 19. Theheating, ventilation, and air conditioning (HVAC) system for use in anexpandable shelter of claim 15, further comprising an air filterarranged in the air inlet vent.
 20. The heating, ventilation, and airconditioning (HVAC) system for use in an expandable shelter of claim 15,wherein the air inlet is arranged substantially proximate to both abottom and a center of the exterior of the front of the expandableshelter.